An article in the Washington Post considers the effect of Omega-3 and-6 fatty acids have on mood and behavior. Here’s an excerpt from The Omega Principle:

By 1999, soybean oil — a major ingredient in crackers, bread, salad dressings, baked goods and processed food of all sorts — accounted for 20 percent of total calories consumed in the United States, according to the U.S. Department of Agriculture. Per capita consumption reached 25 pounds per year. ‘That means that there has been an 1,000-fold increase in [consumption of] omega-6 fatty acids’ over 100 years, Hibbeln says. ‘So we have literally changed the composition of people’s bodies and their brains. A very interesting question, which we don’t know the answer to yet, is to what degree the dietary change has changed overall behavior in our society.’
Flooding brains and bodies with a diet rich in omega-6 fatty acids theoretically could give an unfair advantage to these molecules, allowing them to block omega-3s from getting inside cells and replenishing stores in the brain and elsewhere in the body.

Intrigued by this possibility, Hibbeln charted fish consumption worldwide and compared those figures to rates of depression. In a paper published in 1998 in The Lancet, he showed that nations with the highest fish consumption — Japan, Taiwan and Korea — also had the lowest rates of depression. Nations with the lowest fish consumption — New Zealand, Canada, West Germany, France and the United States — had the highest rates of depression. ‘It becomes an interesting picture across countries,’ Hibbeln says.

Next, he took a look at homicide, suicide and aggression rates and compared them to seafood consumption. Similar patterns emerged. Using World Health Organization statistics, for example, Hibbeln found that men living in land-locked Hungary, Bulgaria and Austria had the lowest fish consumption and the highest rates of suicide, while their counterparts in Japan, Portugal, Hong Kong, Korea and Norway ate the most fish and had the lowest rates of suicide. Men living in the United States, Canada, Italy, Australia and Sweden fell between the two extremes on both seafood consumption and suicide rates.

Since then, Hibbeln has examined patterns of postpartum depression, which provides a particularly interesting window of opportunity for studying the psychological aspects of omega-3 fatty acids. That’s because during pregnancy, mothers are the sole source of an omega-3 fatty acid known as docosahenaenoic acid (DHA) to the fetus. So key is this substance to fetal brain development that the mother’s stores are depleted if she doesn’t consume enough DHA in her diet. In a 2002 study published in the Journal of Affective Disorders, Hibbeln reported that ‘rates of postpartum depression are 50 times higher in countries where women don’t eat fish,’ he says.